1. Field of the Invention
The present invention relates to a multi-optical axis photoelectric sensor.
2. Description of Related Art
A multi-optical axis photoelectric sensor is used as a safety device to monitor entry into a hazard area. A multi-optical axis photoelectric sensor has a plurality of internal light projecting elements or light receiving elements. Further, as a member for defining a spread angle of each optical axis (a spread angle of detection light) of these optical elements, an optical component including a lens or the like is disposed for each optical axis (JP 8-45400 A, JP 2011-216372 A, and JP 2006-107797 A, for example).
JP 8-45400 A discloses a multi-optical axis photoelectric sensor that employs a long body case which is a resin molded article. Specifically, the body case as a resin molded article has a detection window for each optical axis, and a lens member is bonded to the detection window. Further, optical elements (light receiving elements or light projecting elements) are mounted on a substrate which is housed in the body case and extends in the longitudinal direction. The sensor disclosed in JP 8-45400 A can be referred to as a multi-optical axis photoelectric sensor with a relatively simple configuration because an optical component thereof includes only lenses. In the body case disclosed in JP 8-45400 A, the back face side thereof is largely open, and a cover plate is attached to the back face side of the body case after internal components are housed inside the body case. JP 8-45400 A discloses attaching a reinforcement member to the multi-optical axis photoelectric sensor for preventing the warpage thereof. The reinforcement member is a molded article formed by press-processing, for example, a zinc-coated steel plate. The reinforcement member has a length dimension extending from one end to the other end of the multi-optical axis photoelectric sensor. The reinforcement member is fixed to the body case.
JP 2011-216372 A discloses a multi-optical axis photoelectric sensor that has an elongated case body which is a synthetic resin molded article. The multi-optical axis photoelectric sensor of JP 2011-216372 A includes a substrate which has a length extending over the entire area of a box-like case body which is open forward. Optical elements (light projecting elements or light receiving elements) and an optical component including lenses are mounted on the substrate. Further, the optical element substrate is surrounded by a reinforcement member which is made of a metal such as an aluminum alloy, and housed in the case body. The both ends and both sides in the longitudinal direction of the optical element substrate are fixed to the reinforcement member, and some parts of the optical element substrate are fastened to the reinforcement member with screws. A power cable is connected to the optical element substrate. The power cable extends outward from an end of the case body. A cover which is made of a light transmissive synthetic resin is laser-welded to the front opening of the box-like case body.
JP 2006-107797 A discloses a relatively robust multi-optical axis photoelectric sensor. A case of the multi-optical axis photoelectric sensor of JP 2006-107797 A includes an elongated metallic case body having a U-shaped cross section, end caps which block both ends of the case body, and a transparent plastic plate which covers a front opening of the case body. An internal optical component housed in the case is unitized based on a unit of optical axis. Each unit includes a package optical IC in addition to a member for restricting the spread angle of an optical axis and a lens. The one-optical axis optical units are assembled to a support frame side by side.
A multi-optical axis photoelectric sensor is a safety device. Therefore, there has been proposed one that defines the spread angle only by lenses as in the multi-optical axis photoelectric sensor of JP 8-45400 A. However, an object of the regulation is the spread angle of detection light of the multi-optical axis photoelectric sensor. Therefore, a general multi-optical axis photoelectric sensor is provided with not only lenses, but also an optical component for defining the spread angle of detection light. In a multi-optical axis photoelectric sensor that has an internal optical component, as can be seen in JP 2011-216372 A and JP 2006-107797 A, a structure for positioning the optical component is required.
In the multi-optical axis photoelectric sensor of JP 2011-216372 A, there is employed the structure in which the optical element substrate on which the optical component is mounted is surrounded by the reinforcement member which is made of a metal such as aluminum and positioned on the case body which is formed in a box-like shape and made of a synthetic resin, and housed in the case body.
In the multi-optical axis photoelectric sensor of JP 2006-107797 A, the case body which is a metallic extrusion-molded article having a U shape cross section. Further, there is employed the structure in which the optical units each in the unit of one optical axis including optical elements are positioned on the support flame with being arranged side by side, and housed in the case body.
The larger the number of optical axes in a multi-optical axis photoelectric sensor is, the longer the multi-optical axis photoelectric sensor becomes. Therefore, a problem of warpage of a case body becomes more serious. Therefore, as can be seen in JP 2011-216372 A and JP 2006-107797 A, a reinforcement member or a support frame for substantially positioning an optical component is an important element. However, such element is an obstructive factor against downsizing and weight reduction of a multi-optical axis photoelectric sensor.